Circuit arrangement for television receivers



June 3, 1941.

Filed March 11, 1939 2 Sheets-Sheet 1 /0 -AMPL/FIER f5 I :Huu I LINE I Q OSC/LLATUR p DETECTOR V SEPARATOR /4 A MPL/TUDE FRA ME SELECTOR OSCILLATOR AMPLIFIER 1 I I I SYNC. LINE SIGNAL p SEPARATOR /{.LATOR DETECTOR I M SYNC.

FRA ME S ZgA T OR osc/LLA TOR AMPLITUDE SELECTOR 14 w: 3 l0 FRAME I OSC/L 1.4mm AMPLIFIER AMPLITUDE {3 SELECTOR I/ 2 I sYlvc. DETECTOR SIGNAL LINE SEPARA 70, 2 OSCILLATOR INVENTORS ROBERT ANDR/EU HElNl-ZICH BRANDLE' I BY ATTORNEY June 3, 1941. R. ANDRIEU ETAL 2,244,230

CIRCUIT ARRANGEMENT FOR TELEVISION RECEIVERS Filed March 11, 1939 2 Sheets-Sheet 2 FREQUENCY SELECT/ON DEV/CE 20 2/ i 17' 7 l,i w

Vi /{q 8 INVENTOR ROBERT ANDIQ/ U HE/NR/CH BR/TNDLE v BY ATTORNEY Patented June 3, 1941 CIRCUIT ARRANGEMENT FOR TELEVISION RECEIVERS Robert Andriefi and Heinrich Brindle, Berlin, Germany, assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application March 11, 1939, Serial No. 261,384 In Germany March 14, 1938 3 Claims. (c1. 178-75) A circuit arrangement for television receivers has already been proposed in which the sawtooth generator for the line scanning is blocked for the duration of the synchronizing impulse for the vertical or frame deflection of the oathode ray beam. The frame deflection is hereby understood to mean the deflection in the slow image coordinate (vertically), whereby the transmission may be one with the ordinary line sequence, or a line skip transmission. The blocking was carried out in accordance with the older suggestion to'the'e'n'd that after completion of the synchronizing impulse for frame deflection, i. e., at the setting-in of'the line impulse for the new line, there will be obtained within a possibly short time period the built-up state of operation in the line saw-tooth generator.

In accordance with the invention, in a tele vision receiver whose saw-tooth generator for the coordinate of the frame trace has a tube in' which a current flow is effected for initiating the frame trace return, a potential shall be produced during the entire duration of this current flow through which the channel will be blocked in which the frame impulse and the line impulse can produce a'control potential at the said tube and which potential also blocks the line saw tooth generator proper.

Before explaining a mode of construction according to the invention and some improvements which are of advantage in connection-with the invention, there will be briefly given the reason for carrying out the said blocking during the entire duration of the current flow through the controlled tube.- In this connection it should be borne in mindthat the separation of the frame impulse from the line impulses has been carried out in virtually all hitherto known tele-' vision receivers in that at first'an amplitude difference is provided between the frame impulse and'the line impulses and that thereafter this amplitude difference is evaluated. The first step of providing an amplitude difference is carried out in a so-called frequency selection arrangement, and the second step of evaluating this amplitude difference is carried out in a so-called amplitude selection stage. Now if in accordance with the present invention the channel leading to the frame saw-tooth generator is blocked during the entire time in which the controlled tube of the frame saw-tooth generator has current, it is possible in the blocking oscillator circuits or in similar circuits almost exclusively in use today, to attain the amplitude selection stage for the said tube of the frame saw-tooth generator through a corresponding biasing potential of the controlled grid of the blocking oscillator, whereas without the said blocking a special tube would be required. In fact if a blocking in accordance with the present invention would not be carried out danger exists that through a line impulse which follows the frame impulse the tube of the vertical saw-tooth generator would be subjected to an additional impulse which could disturb the time pattern of the plate current in this tube. In order to exclude such influence upon the respective tube on the part of the line saw-tooth generator also by inductive means, it is proposed as already stated above also to block the line saw-tooth generator, and this for the total time of the current flow in the tube and not solely during the time in which the frame impulse lasts such as was done in accordance with the older suggestion. The duration of the current flow in the controlled tube need not at all be identical to the duration of the frame impulse, in fact when employing for instance a blocking oscillator circuit the controlled tube of the frame saw-tooth generator may conduct current during a time period which is much longer than that of the frame impulse. 7

The invention may best be described by referring to the drawings wherein:

Figures 1, 2 and 3 show various schematic forms of receiving systems.

Figured; shows a system in accordance with the present system.

Figures 5a and 512 show operation curves.

Figure 6 shows a modification of a portion of Figure 4, and

Figures 7 and 8 show curves of operation relating to Figure 6.

It should be remarked at this place that the invention can be applied to all hitherto known and proposed receiver types which may be classifled in the'following manner: In a receiver type schematically shown in Figure 1, a high frequency amplifier or intermediate frequency amplifier lll' feeds into a detector circuit H having connected thereto a separation arrangement l2 which separates the impulse mixture from the image content. A branch off point P is in back of the separation device and from which a chan; nel leads across a frequency selection circuit with following amplitude selection stage l3 to the frame or vertical saw-tooth generator l4 and another channel to the line saw-tooth generator l5. In this latter channel an arrangement for separating the frame'impulse can be inserted but this is not shown in Figure 1. In a receiver according to Figure 1 the blocking according to the invention is therefore to act ahead of the branch off point P if it is to be effective for both channels, or it should act in back of the point P in each individual channel.

In a second receiver type shown in Figure 2 which differs from that shown in Figure 1 in that the branch off point P is situated between detector H and the separation device thus requiring two separation devices l2 and 12'', the same is to be said about the blocking namely that either a single blocking point is situated ahead of P, or when in back of P there is-to be a blocking point in each channel.

In a third receiver type shown in Figure 3 the frequency selection circuit i3 with following amplitude selection stage is connected to the line saw-tooth generator !5 and the blocking is to act at the line saw-tooth generator but at no later place. As compared with this it would not be sufficient in the sense of the invention to have the blocking act in i3 in Figure 1, or in if! or 13 in Figure 2, and in It in Figure 3.

A mode of construction according to the invention is shown in Figure 4 of the drawings. In this figure item I6 is a transformer across which a detector circuit is fed with the high frequency potential or intermediate frequency potential modulated with the image content and with the synchronizing impulses. Item I1 is a detector tube and I8 and I9 represent two loads resistors each having connected in parallel thereto a respective smoothing condenser 20 and 2] respectively. In case of the method of so-called gap synchronizing (synchronous impulses in the direction which is blacker than black by interruption of the carrier wave, i. e. positive transmission), the potential for the control grid 22 of the image reproducing Braun tube 23 can be derived immmediately at the left end of the resistor 18. At the right end of the resistor IS the line impulses appear with positive polarity, i. e., the potential at this place increases at each front of a line impulse. Item 24 designates a self blocking oscillation generator feeding across the line 25 the end tube of the line saw-tooth generator. A further self blocking oscillation generator for the frame deflection is designated by 26 and is fed at the screen grid with the mixture of line impulses and frame impulses formed by the frequency selection circuit 21. As explained in regard to Figures 1 to 3, it is immaterial as such whether the frequency selection arrangement 21 is fed from the right end of the resistor i9 whereby an amplitude selection stage l2" for the, separation of the synchronizing impulses from the image content lies ahead of the frequency select-ion arrangement (Figure 2), or whether only a single amplitude selection stage l2 for the separation of the image and impulses is employed and the impulse mixture is obtained from the line saw-tooth generator l'5 (Figure 3). The saw-tooth generator for the frame deflection consists in addition to the blocking oscillator circuit 2B of the resistors 28 and 29 and condenser 30. During the time periods in which the blocking oscillator 26 has no plate current the condenser 30 will be charged across the resistors 28 and 29, and this condenser will be discharged during the plate current impulses in the blocking oscillator 26. Then a potential increasing in a linear fashion appears during the period of the frame deflection at the upper layer of the condenser 30 to which the frame deflection coil can be connected across a tube, or to which the deflection plates for the frame deflection coordinate are connected across a push-pull amplifier. The resistor 29 serves in a manner known as such for producing an impulse shaped voltage component during the pause in the frame deflection, said voltage component being added to the saw-tooth potential at the condenser 30 in order to produce a non-distorted saw-tooth de flection despite the self inductance of the deflection coil or of the distributed capacity of the leads of the deflection plates. During the discharge of the condenser 30 across the blocking oscillator tube 26 the potential drop through the resistor 29 has the direction indicated by the plus and minus signs in Figure 4.

The potential pattern appearing in back of the frequency selection circuit 21 has for a single 7 impulse sequence according to Figure 5a, the

.impulses following the frame impulse.

pattern as shown for instance in Figure 511. If, as already stated above, this potential pattern is applied to the screen grid of the blocking oscillator 26 without the insertion of an amplitude selection stage containing a special tube, the plate current pattern in the blocking oscillator which has a longer time period than the frame impulse, could be disturbed by the line impulse or line impulses following the frame impulse and by the corresponding potential pattern at the frequency selection circuit. This is due to the fact that the plate current of a-screen grid tube depends in fact on the screen grid potential while this screen grid potential is determined by the potential at the frequency selection circuit. If, however, as suggested in accordance with the present invention the passage of impulses to the frequency selection circuit 21 is blocked during the period of the plate current impulse in the blocking oscillator tube 26, the frequency selection circuit will not be influenced by the line This measure is of importance especially in line skin or interlace transmission since in this case in two successive frames the first line impulse follows the preceding frame impulse in different time spaces. A different time of the anode current impulse in the blocking oscillator 25 would in fact jeopardize the exact relative position of the two frames in the receiving image. The connection line 3! causes the potential of the entire detector circuit |'12| to become lower during the plate current impulse in the blocking oscillator 26, and therefore such a high negative biasing potential (namely the potential drop through the resistor 29) would be applied to the frequency selection arrangement 21 as well as to the line blocking oscillator 24 that the line sawtooth generator can neither operate nor can the freouencv selection arrangement 21 receive a potential. The aim of the present invention is thus in fact achieved, namely to have the plate current impulse in the blocking oscillator 25 takin its proper course once it has begun without influenc ng it further.

The circuit shown in Figure 4 is further remarkable inasmuch as it is possible to achieve the return blocking and the production of an impulse component in the frame saw-tooth b means of single resistor, namely by the resistor 29. Principally it wou d also be possible to derive the potential for the return block n in a dif erent way from the blockin oscillator tube and to emp oy the resistor 29 solely for produ n the impulse. component.

The leading-in of the return blocking potent a at the connection point between the resistors l8 and t9 of the detector circuit as shown in Figure 4 aside from the desired end of blocking the frame saw-tooth generator and line saw-tooth generator, entails the further advantage that the cathode ray tube will likewise be blocked during the plate current impulse in the blocking oscillator 26, i. e. during the ray return in the vertical direction.

Furthermore it is of advantage to choose the time for the return blocking somewhat longer than that for the plate current impulse in the blocking oscillator 26. This is advisable since in this way the blocking of the ray in the cathode ray tube will be definitely terminated only after the vertical or frame return is completed. In order to have the return blocking lasting somewhat longer than the duration of the plate current impulse a condenser 32 may be placed in parallel to the resistor 29 such as shown in Figure 6 (which is a portion of Figure 4) and the time constant of 29 and 32 can be so chosen that the potential at the upper end of the resistor has approximately the pattern shown in Figure 8 instead of the pattern in the circuit according to Figure 4 as shown in Figure '7.

The circuit described in reference to the Figures 4 and 6 not only may be employed for the method of gap synchronization, but also for the case in which the synchronizing impulses lie in the direction blacker than black and are transmitted by an amplitude larger than the image content (negative transmission). In the latter case in the circuit according to Figure 4 it is necessary simply to connect to the left end of the resistor I8 the blocking oscillator for the line deflection and to connect the control grid 22 of the cathode ray tube to the right end of the resistor I9. Otherwise all other deliberations hitherto made remain unchanged.

The described return blocking is not only of advantage when using a blocking oscillator circuit in the frame or vertical deflection generator, but also in every case in which the frame deflection generator contains a tube circuit which, following the excitation by the changed frame impulse, furnishes a current impulse whose course can still be influenced by potential variations applied from the outside. There belongs among these tube circuits also for instance a tube relaxation circuit having two discharge tubes coupled in opposition across a resistancecondenser combination.

We claim:

1. In a television receiving system wherein picture and synchronizing signals are received with the synchronizing signals having an amplitude greater than any picture signals, a cathode ray picture reproducing tube having a control electrode, means for applying the received pic ture and synchronizing signals to the control electrode with the synchronizing signals extending in a negative direction, a horizontal deflection voltage generating means, means for applying the received signals to the horizontal deflection voltage generating means with the synchronizing signals extending in a positive direction to control the frequency of operation of the generating means, a vertical deflection voltage generating means including a resistance and a condenser,

means for connecting one end of the resistance to one plate of the condenser, means for connecting the other end of the resistance to a source of positive potential, means including an impedance for connecting the other plate of the condenser to a point of fixed potential, means for intermittently and substantially instantaneously discharging said condenser to develop potential impulses across said impedance and means to apply the developed potential impulses to the horizontal deflection voltage generating means superimposed upon the received signals whereby operation of the horizontal deflection generating means may be discontinued for a portion of the operating cycle of the vertical deflection voltage generating means.

2. In a television receiving system wherein picture and synchronizing signals are received with synchronizing signals having an amplitude greater than any picture signals, a cathode ray picture reproducing tube, a horizontal deflection voltage generating means, means for applying the received signals to the horizontal deflection voltage generating means to control the frequency of operation of the generating means, a vertical deflection voltage generating means including a resistance, a condenser and an impedance, means for connecting the resistance, condenser and impedance across a source of potential, means for intermittently discharging said condenser to develop potential impulses across said impedance, and means to apply the developed potential impulses to the horizontal deflection voltage generating means whereby the horizontal deflection voltage means may be discontinued for a few cycles of its operation during the discharge of the condenser.

3. In a television receiving system wherein picture and synchronizing signals are received with the synchronizing signals having an amplitude greater than any picture signals, a cathode ray picture reproducing tube having a control electrode, means for applying the received picture and synchronizing signals to the control electrode with the synchronizing signals extending in a negative direction, a horizontal deflection voltage generating means, means for applying the received signals to the horizontal deflection voltage generating means with the synchronizing signals extending in a positive direction to control the frequency of operation of the generating means, a vertical deflection generating means including a condenser, means including a resistance for connecting one plate of the condenser to a source of positive potential, means including an impedance for connecting the other plate of the condenser to a point of fixed potential, means to intermittently discharge said condenser, to develop potential impulses across said impedance, and means to apply the developed potential impulses to the horizontal voltage generating means and to the control electrode of the cathode ray tube whereby a horizontal deflection voltage generating means and a cathode ray tube may be rendered incomparative for a relatively short period of time.

ROBERT ANDRIEfI.

HEINRICH BRKNDLE. 

